Interface Localization in Thin Films

by Jang, Hyunbum

Abstract (Summary)

Restricted Item. Print thesis available in the University of Auckland Library or available through Inter-Library Loan. Monte Carlo simulations have been performed for different types of thin films under the action of competing surface fields with the same magnitude but opposite direction. For thin ferromagnetic Heisenberg films, a single-site anisotropy ?, and an exchange anisotropy ? were used in the model Hamiltonians. In the Ising limit of each model ? ? ?and ? ? 1, the interface localization tansition first seen in the thin ferromagnetic Ising film with competing surface fields can also be observed in the thin ferromagnetic Heisenberg films. A non-zero magnetization of the film is observed below a critical temperature Tc that can be associated with a localization of the interface between regions of positive and negative magnetization near the film surface. A degeneracy in the magnetization profiles exists between states of positive and negative total magnetization at low temperatures. Whereas, in the Heisenberg limit of the models, ? ? 0 and ? ? 0, no spontaneous magnetization of the film is observed and the magnetization profile across the film is antisymmetric, slowly varying from positive magnetization on one surface to negative on the other. For thin Ising films with competing surface fields and a bulk transverse field ?, an interface localization transition with an associated spontaneous magnetization of the film is also observed below Tc. However in the limit of ? ? ?, no spontaneous magnetization of the film is observed. Monte Carlo simulations have been extended to study the phase behavior of thin uniaxial liquid crystal films with competing surface fields. The model Hamiltonian is a combination of the Lebwohl-Lasher model and the anisotropic Heisenberg model with a ferromagnetic exchange anisotropy ?. The interface localization transition observed with the competing surface fields is substantially influenced by the size of the nematic coupling constant ? and the ferromagnetic exchange anisotropy ?.